Friday, December 30, 2016

Building the Bitx40 ~ The how to for the newcomer!

12/31/2016 ~ Life is Too Short for QRP!

So Ok guy's here is how to boost your signal (using an external linear amp) so you can be heard and duck those dreaded repeats of your name and QTH.

It is pretty simple to implement. All you need is three diodes if you include the 1N4148 snubber diode across the reed relay coil, a RCA phone jack and a terminal strip. One side of the relay contact is simply grounded by soldering to the PC board that holds the reed relay (yep super glued upside down to a scrap piece of PC Board). The other lead goes to the rear panel mounted RCA jack. The two 1N4007 isolate the circuits from each other. With this arrangement I am able to drive my SB200 to 100 watts output. Pretty cool.

73's
Pete N6QW

73's
Pete N6QW

About a month ago I agreed to give a Skype presentation to a local ham club known as the Ventura County Amateur Radio Club (VCARC) on the subject of homebrewing. Hey I am really good at soldering my fingers together so I guess I sort of qualify as a homebrew radio enthusiast. In the course of discussing the presentation with the club president Joe, K6NE, I suggested that the club might want to engage in a group project using the Bitx40 board available from India for the amazing price of $45 shipped to your door. Bitx40 is the link to the website where the radio can be purchased.

[The club presentation will take place two weeks from today and so I have been under the gun to get everything completed.]

For your $45 you get a complete built radio transceiver board with all of the controls, connectors, wire harnesses and even a microphone element and PTT. As shipped the radio is on 40M and is capable of over 5 watts output. The means of frequency control is a voltage tuned oscillator using a panel mounted pot to change the frequency. It works but a better alternative is to purchase the Digital VFO kit and LCD which adds another $14 --so less than $60 and you have quite an impressive radio. I purchased my board in late November 2016 and the Digital kit was not offered so I rolled my own Arduino/AD9850. The add on kit uses the Si5351 PLL.

Thus the builder (in this case the club members) provide the value added by integrating the parts and pieces into an enclosure and along the way learn about the nuts and bolts of the radio. VU2ESE developed this kit specifically to learn about what makes up a transceiver and to experiment to your hearts content and indeed he has met that goal.

To aid the club with this project I volunteered to create a series of webpages hosted on my website so that in addition to the excellent information on the http://hfsigs.com website that I would provide detail on how to execute the actual build. My webpages have many links to where you can purchase enclosures or special tools and even a grounded soldering iron.

In the early days most ham stations were entirely home built and thus many of the fundamental hand tools and parts were in the junk box. But today it is "flash the plastic" and in two days UPS has a black box radio sitting in your shack. So to actually build something takes a lot more effort. My webpages make it an easier task. Hey are you looking for a QRP SWR bridge (there is a link to the DX Engineering MFJ Model 813). Well in my case I built my own but not everyone wants to do that.

So here is the link http://www.n6qw.com/Bitx40.html There are sub links that explain how to metal bash, detail on the wiring (including a link on where to buy the wire) and the check out process. Again my pages are to supplement what is on the www.hfsigs.com website.

I have made four contacts with this radio and this has been a fun project but now I need to move on and this will be the last posting on the Bitx40.

Tuesday, December 27, 2016

The Bitx40 Project --a good rig for just a few dollars!

12/28/2016 ~ First QSO on the new Bitx40. Now at Four Contacts Total!

Listen to the 1st QSO on my new Bitx40. Click the link below. General impressions are that it is a good value for $45 but get the digital VFO add on for another $14. Now that a successful build has been achieved time to move on to another project. Oh for the microphone enclosure (seeing as the electret cartridge is included) I took a defunct microphone and adapted it to the simple cartridge. It seems to work OK. I missed my by Christmas QSO goal by a couple of days but it is working none the less.

Found out why you need the coupling cap out of the DDS! Initially I was advised to disconnect L4 from the pin header. Don't do that! Leave everything as built. The reason I needed a blocking cap was that the hot side of the Pin Header goes right into the base --any RF signal must have the blocking cap. In VU2ESE's Digi VFO there are blocking caps coming off of the clocks. So don't make that mistake.

Additional contacts include K7JUK, KE7LK and KJ6IX. These include stations in Nevada and Arizona. Most signal reports were Q5, Punchy Audio but not even moving the S Meter. What do you expect from 5 watts?

73's
Pete N6QW

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I have been working on building the Bitx40, a neat rig from VU2ESE see www.hfsigs.com. Finally got my unit receiving today using the AD9850 for the LO. Below is a still shot and below that a you tube video. I initially had a problem that the DDS wouldn't work and so I shifted to the varactor VFO and that worked so I knew the board was OK. Man talk about drift. Worthless is a good word. Then I put a cap in series with the DDS and it worked. Without the 10NF cap the DDS output was being shunted to ground.

I would strongly recommend not using the on board VFO for anything other than testing the rig. Either build a solid Analog VFO like N2CQR or just jump to Farhan's add on kit that for $14 additional which gives you the digital capability. Don't waste your time with the on board VFO other than for test purposes.

Monday, December 26, 2016

FPM5 ~ How to save from pulling out your hair!

12/27/2016 ~ Revised Simulation

This is the value of LT Spice as you can modify the design without soldering one wire. Many options and iterations can be evaluated and the bonus --it can be done quickly. In chasing the elusive problem of too much gain at lower frequencies and not enough on the higher bands, I am being convinced that it now is not the specific circuit I thought the problem. But at the same time there is an opportunity to optimize that circuit. So that is what I did at 4:30 AM this morning. My daylight hours are taken up with caregiver duties so I have found working in the early morning hours does provide some opportunity. I am trading sleep for ham radio design work.

Noteworthy in the new design is forcing the impedance matching by going back to the original primary winding (8 turns) and changing the secondary to two turns. The matching is now 64/4 so that it is a 16 to 1 transformation. The secondary is terminated in 50 ohms and that reflects back as 800 Ohms in the primary. I now placed a 820 Ohm resistor across the primary. I also played around a bit with emitter feedback. These changes are intended to "flatten the gain" yet provide a stable gain over a wide frequency range.

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In looking at the gain plot below, the delta change at either end of the intended operational range (75 to 15 Meters) from the center range is about 0.4 dB so this is relatively flat. I will make those changes and then evaluate the real circuit performance versus the predicted performance. This plot looks to be more in line with the desired "flat" performance over the operating range.

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Stay tuned and I will report the results.

So now that still leaves us with the problem of too much gain at the lower end and not enough at the higher range. My attention is now focused on the prior stage and that can be done by looking at the input to this amp and see the signal levels. Ahead of this is the band pass filters and ahead of that the SBL-1 Rx Tx Mixer stage. One other area is the signal level coming out of the Si5351. I have not looked at the signal levels from the LO. The LO is operating over the range from 12.5 MHz (75M) to 30 MHz (15M). The output should be fairly constant but that may be a bad assumption. I do know that is a problem with the AD9850. Once the prior stages have been evaluated and a conclusion reached then the circuit elements upstream can likewise be evaluated.

Happy New Year!

73's
Pete N6QW

12/26/2016 ~ Late Update! Synopsis --that did not work too well.

Despite having the LT Spice simulation shown below the change in hardware did not resolve the higher gain at the lower frequencies and anemic gain on 20/15 Meters. So the good news is that the issue is elsewhere. What I didn't do is to plot the actual gain coming out of just this pre-driver stage and then see what the plots look like in comparison to the LT spice plot. But I am now suspecting the issues are elsewhere. The positive news is that we are eliminating possibilities!

73's
Pete N6QW

12/26/2016

Well it has been nearly a week since getting the FPM5 in a box and I can truly say this has been some ride. Firstly the adage "if it ain't broke don't fix it" rings true. The rig worked great "al fresco" hay wired into place but once getting it into a box with proper grounding and short leads it is then that the warts show up. Thus I have been working down a list of issues and one by one these are being resolved.

Finally I was at the point of why there was way too much intermediate RF gain at 75 Meters and the transmitted signals were anemic on 20 & 15 Meters. This is where we can be tripped up by thinking we know something, discounting it and then keep coming back to the same point with nothing being changed.

A long time ago I developed a circuit that is a relay switched bidirectional amp consisting of two legs and employing the ubiquitous 2N3904 NPN transistor. This device is usually available in quantities for a price around 4 cents. You can beat that! Typically my bidirectional design had one leg be the receiver RF amp on Rx and on transmit the other leg was the pre-driver for transmit. This has served me well and is typically my "go to" circuit. I guess my experience with the KWM-4 should have been a large blinking sign but some how my brain ignored it until now.

Finally today I decided to put my circuit to the acid test using LT Spice. About five years ago I hay-wired it together --it worked and I moved on. But I had never subjected the design to a rigorous evaluation. That was my first mistake! Simulating the circuit with new values provides a rigorous look at a real gain plot and this looks much better.

Here is what I observed. First there was way too much inductance on the transformers. By empirically reducing the turns on the primary to 5 turns and the secondary to 2 turns the impedance transformation was 25/4 = 6.25. The secondary side always sees 50 Ohms because of the fixed resistive load of the 100 Ohm fixed and 100 Trim pot in parallel. The output is taken off of the center wiper through a 10NF cap. This says the primary load is reflected back into the secondary as a load of 300 ohms. The next thing I did was to look at the emitter of the 2N3904. Initially I had a 50 Ohm resistor in parallel with a 100 NF cap. I tried adjusting that value and with 1K in parallel with the 100 NF this seemed to provide a flatter curve and shifted the center hump past 10 MHz which now aligns with the intended operation on 75, 40, 20 and 15 Meters.

The modified circuit is presented below: Note the two 50 Ohm resistors in series simulate the 100 Ohm trim pot with the center wiper at midpoint.

Gain Plot with Inductor and Resistor Change

You can simulate the circuit and verify my values and plot. My next step is to wind a new transformer with the 5 and 2 turns and replace the emitter resistor with actually a 1K pot with the 100 NF connected to the center wiper. This will give me an additional opportunity for evaluation. I will post the results but this looks promising as a reason why I was early on seeing the imbalance in the gain across the HF ham bands. This does not fix the problem on 10 Meters but my added band since I am only using 4 of the 5 bands that can be activated would be for 60 Meters and that falls within the curve.

Also important is the phasing of the turns: The output winding that is nearest the collector is the "Hot" side and the other side nearest the 12 VDC feed is Ground. This is shown as the dots on the schematic. BTW the original primary winding was 8 turns and that yields an inductance of 22.4 Micro-henry. So three fewer turns drops the "L" by almost 2/3!

Thursday, December 22, 2016

The FPM5 is in the box but has a few issues. You know the drill: Worked great 'al fresco" but now that it has been made neat there are some RF feedback issues! Sometimes it is good to take a break and just do something else.

[See video of FPM5 at the bottom of the section 12/23/2016.]

So here is the something else. My sister whose OM is also a ham sent me an early Christmas present and I must admit it has really captured my attention. By way of history I was born in a small town in western Pennsylvania (PA) not far from the city of Pittsburgh. The name of the town was New Kensington. While PA was known for coal and steel it was also home to aluminum manufacturing which of course was in New Kensington. Yes those Alcoa pots and pans were at one time made right there. The Alcoa Research Labs were also located there. Much of the area economy was derived from those working at Alcoa.

So the book I received is about New Kensington history but a different side of the economy. After all, those folks making all that money needed a place to spend it! The name of the book is "Little Chicago: A history of organized crime in New Kensington, Pennsylvania". Think of the movie "The Godfather" only transplanted to western PA. The author is Dennis L. Marsili, ref: ISBN 978-0-692-53892-0. Mr. Marsili spent many years as a detective on the New Kensington Police Department thus has a first hand knowledge of the detail.

What has captured my attention is that I was growing up in that town right when all of the "action" was taking place; but was only vaguely aware of this other side. Having an early insane interest in electronics can keep you away from the real world.

Some of the people mentioned in the book I have met. In one case an individual high up in the "organization" had children going to the same high school I attended and one of the children was a classmate and friend. On one occasion I was introduced to the father but somehow never added two and two.

The author presents a side of the two brothers that headed the organized crime family that in reality provided a stabilizing force that actually made the town safe. Nothing happened without their approval! There was a sequence in the book about a store owner being robbed and the first person called is not the police but an individual with connections --several hours later all the stolen merchandise was returned --no questions asked. In 2015 our home here in California was robbed and in speaking to the police detective assigned to the case -- I said to her, if I was back in New Kensington, I know a guy who knows a guy and in short order I would know who did this. She (also being Italian) said that works very well there but not here.

Another sequence dealt with integration. In the 1960's segregation in the USA was still in evidence and New Kensington was no exception. With the passage of the civil rights act and the strength of the civil rights movement the last thing the two brothers wanted was Federal intervention. Mind you these two brothers had no more than a 7th grade education but were astute business men and made a conscious business decision. They simply made it known that the businesses should be integrated. I would like to say the transition was overnight --maybe not, but close. Done deal. The author leads you to ponder that organized crime was far better at handling social issues than the organized government. Just think of the debate that would take place, the lobbying of special interest groups, the back door deals and then finally a chaotic vote. No fuss, no muss -- it was good for business and a done deal.

With the passing of the two brothers the town is no longer a "safe" place and alas Alcoa has also moved out. What you see today is a rust belt city with the attendant decay, high crime, and a just shadow of what was once a thriving community.

It is a great read to me as I lived there and the places, locations and names are very familiar to me and in some cases has filled in the blanks on why certain things happened or didn't happen. There is a even a Cuba connection and gun running.. So it was more than regional in its scope. The read has served me well as I now have had a sufficient diversion from the FPM5 to think about RF feedback problem resolution.

Thursday, December 15, 2016

Wiring is 99% Complete!

Smoke Test Passed!!!! Late Breaking News.

It is ALIVE! More tests to follow.

73's

Pete N6QW﻿

The only remaining wiring is to connect the circuitry so that when you hit the PTT or place the rig in TUNE, the Color TFT displays "ON THE AIR". How cool is that? There are two photos of the rear deck area one has the shield over the PA and the last one has the cover in place. Stay Tuned for the Smoke Test Possibly on 12/16/2016. The wiring mess has now been better organized!

Wednesday, December 14, 2016

Working Two Projects (FPM5 & Bitx40) Simultaneously!

As I wire up the final configuration of the FPM5 I am also working on building the Bitx40. Mind you this is being done under severe time constraints associated with my caregiver duties. So indeed it is a high wire balancing act. There is frustration in being able to only accomplish so much in short blocks of time. But in some ways this is not all bad as it forces you to time manage and to "noodle" what are the most efficient ways of doing the hardware tasks.

Just so you know here are update photos of the final wiring status of the FPM5. Keep in mind the rig was purposefully built in modules and this pays off "big time" in that I am able to easily remove modules and this facilitates the wiring process. It still looks like a jumbled mess -- but it is an organized mess.

After about a day of intermittent work the above now looks like below.

Still a mess but getting better! Yes I have installed "my version" of the active reverse polarity protection --lower right hand corner.

Now to the Bitx40. In the SS Podcast#191, Bill N2CQR spoke at length about the Bitx40 which is a complete built SSB rig being sold by VU2ESE for the amazing sum of $45 shipped from India. During that podcast I mentioned I had one coming and mine has arrived and I have done some work on my build. This can be seen below --yes Juliano Blue is very evident.

At this stage the hardware is mounted and previously I had programmed the Arduino/AD9850 which will be used for the LO. The case was something store bought about 6 years ago and is nothing more than a 6X10X2 aluminum chassis painted two tone. The front panel is of course a cool blue color.

But there is another side to this project in that I will de doing a Skype presentation to a local ham club in mid January and in preparation for that Bitx40 pitch have created a series of web pages on "How to take the Bitx40 as supplied and make it like the photo above. Here is the link to the web "Resource Page"

A great deal of midnight oil was spent on this page as there are links to the vendors and parts that are used outside of what is supplied by VU2ESE. As an example ditch the audio control and switch as supplied. The shaft on the pot is larger than 1/8 inch and smaller than 1/4 inch. I replaced that hummer with a standard 1/4 inch shaft 10K audio taper pot and added a mini toggle switch for ON/OFF. The resource page will take you to the vendor pages that detail the pot, the toggle switch and even the knob! There are two options for a commercial enclosure and the same process opens the vendor pages for the options (one is from Jameco and the other from Mouser). The only thing I haven't done is build it for you.

A Note for those so inclined to send me comments all of the pages are not complete! Pages covering the first phase will get you to the point of having the hardware to build the Analog VCO version. Later pages will detail the mechanical construction, the wiring and even building the Arduino/AD9850. The effort so far is to introduce the project and provide the critical links for the additional hardware.

Sunday, December 11, 2016

FPM5 ~ Protecting All of the Hard Work

One of the sickest feeling you can have is to plug in a new rig to 12 VDC and watch it go up in smoke as you realize you had the leads to the power supply reversed. yes I have done it and I am sure you have too.

In the SolderSmoke Podcast #191 Bill, N2CQR and I were talking about this subject specifically in regard to the new Farhan, VU2ESE's rig the Bitx40. Bill having one strongly encouraged the addition of reverse polarity protection using a diode.

Of course as usual any time you make a suggestion you get the naysayers who lurk the various reflectors whose sole goal in life is to spread negativity about anything. Typically these individuals have never built ANYTHING and think they are experts! They are often quick to pan a solution and they quickly jumped on Bill!

I am facing the same situation with my FPM5. Man I have months invested in this rig and the last thing I want to see is it smoking from wrong polarity being applied. But I wanted something more than a diode, otherwise I am sure I would have the same level of negativity applied to me.

So while awaiting for mass to start this morning (instead of reflecting on the holy religious event that was about to start) my mind drifted onto the subject of reverse polarity protection. I have come up with two schemes and these are presented below.

Both schemes involve the use of a diode and a relay. The relay I happen to be using is a very small American Zettler DPST type that is good for 10 amps. These were bought surplus but many of the larger supply houses sell them for about 60 cents and the 1N4007 I bought for 5 cents -- so for $0.65 you have protection.

The first scheme is what I call passive in that the relay is only energized when you have the wrong polarity connected to the right terminals. When this happens the relay essentially opens and disconnects the rig from the supply. This scheme is ideal for QRP ops as there is literally no current draw other than leakage current under normal operation. So there should be no complaints about wasting milliamps. You hit the power switch and power is applied to your rig.

The second scheme is more appealing to me in that it is an active approach. You hit the power switch and power is applied to the radio! But if you reverse the leads despite hitting the power switch there will be no juice applied to the radio.

Monday, December 5, 2016

FPM5 ~ The Final Assembly is on the Threshold!

December 8, 2016 ~ TRGHS (The radio Gods have spoken)

Something weird happened today! At about 10:00 AM two boxes showed up at my door step. One was the wire needed for wiring up the FPM5 plus a couple of 8X2 LCD's and some other parts. Now I can get started in earnest with the final wiring phase of the FPM5. The second box was addressed to me complete with my call sign and the return address was from a person in New Mexico. That seemed strange as I hadn't purchased anything not even on eBay.

So I open the box and contained therein are three rolls of solder. Hey cool something I can use --I am burning lots of solder these days. But I was mystified. Then I had a TRGHS moment and realized what was going on.

Several weeks ago I checked into the Albuquerque Boat Anchor Net. The check in process involves identifying your station and what sort of boat anchor gear you are running. I could hardly contain myself as I explained that the basis of my rig was the hallicrafters FPM300 which had been re-incarnated as the FPM-5. I directed those on the net to look at my QRZ page for details. Well as it turned out every time the net meets there is a secret rig selected and if you are running that gear you get the prize. The night I checked in, the mystery rig was anything hallicrafters --- Boom that is what I was running and thus being the only person running that kind of gear the prize was all mine --which in this case was three rolls of solder! The actual prize was not announced only that I won --- yes TRGHS. Thank you Boat Anchor Net!

Pete N6QW

December 7, 2016 ~ More Final Assembly Installations

Today I installed boards in the box! Lots of measuring and hole marking and then final drilling. One serendipitous event was that initially I bent up (using my vise [or for my friends in the UK my vice]) a U shaped heat sink. Since the 5 watt PA board will be mounted directly to the back apron, the bent up sheet metal would now be redundant. But by using some aluminum [aluminium] pillars this heat sink has been turned into a shield cover over the PA board. Nice! Below are some of the installations into the case. Believe it or not -- I am out of hook up wire an am now awaiting a shipment. This will hold up final wiring and integration.

Note the Shielded PA Enclosure on the back apron

Shielded PA Enclosure

There are two more board installations including the mainboard and the power supply board. The plan is to vertically mount the power supply board on the back side of the LPF board. There are some other smaller installations such as terminal strips and a 4 P DPDT relay

I have built and installed the 15M BPF but now need to address the 15M LPF. There is one open position on the BPF and LPF Boards. Instead of 10 Meters I may install a set of filters for 60 Meters. Stay tuned.

73's

Pete N6QW﻿

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December 6, 2016 ~ Band Switch Demo

December 6, 2016

I really think it is all going to fit in the box. Now before you jump on the comments about why did I make it so big and why couldn't the box have been smaller, let me share some experience with you. In the Solid State Design for the Radio Amateur (SSDRA a book which I consider a more useful publication than EMRFD) the very last project from W7ZOI is what is called A Competition Grade CW Receiver which later morphs into a trans-receiver.

I built that jewel only went to extremes and built every module into an individual aluminum mini-box. All power was passed into the boxes using feed through capacitors and all signals in and out were via RCA connectors. Enter the first problem --if you wanted to adjust something or troubleshoot a problem, this required a major disassembly. Frankly it was quite hard to get to some of the circuit wiring once the boards were installed in the boxes. The really great idea was a disaster! One time in that rose garden and you soon know the roses look beautiful but the stems have thorns!

So a word or two about shielding. I marvel at how some complete radios are built on a single circuit board and there is no shielding and there doesn't seem to be feedback problems. The newest rig, known as the Bitx40 from Farhan VU2ESE has a whole transceiver on a board 5 X 5 inches and seems to have resolved that issue. I on the other hand am not always so lucky. But I do strongly feel shielding is a good idea as is a common ground plane. Thus my approach to CNC the circuits on common ground plane modules is part of my shielding approach.

Another is some physical separation to reduce the possibility of unwanted coupling. Thus there are three reasons for the box size.

Ease of maintenance and troubleshooting -- I will be able to get scope probes into the various circuit boards to facilitate maintenance and repair.

To provide physical separation between various circuit elements to reduce unwanted coupling. But there also is a consideration of actual circuit flow and how signals are routed. Experience gained from the Tri-Band XCVR built in 2009 and the KWM-4 built in 2012/2013 has played a major role in the decisions regarding the FPM5.

The use of copper boards provides a shielding factor and the physical placement provides that shielding and the fact that the boards are copper and connected to the main chassis, we have one common ground plane.

So here are some shots of the additional fit checking and board placement. The Low Pass Filter Board and Band Pass filter board will essentially be at right angles to each other and physically separated. The bi-directional (Rx RF Amp and Tx Pre-Driver) module is shielded from the main board and the Tx driver stage is a short physical distance from this board. This will keep RF leads to a minimum.

Rough Location of the Boards. The Final Tx RF Amp is mounted on the back wall of the case.

It is all coming together! But right now it looks terrible!

73's

Pete N6QW﻿

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December 5, 2016

Some really good news -- thanks in large measure to the efforts of Greg, VK1VXG, I now have the capability of when you move the band switch to a new band the new band starting frequency will display. Thanks to all who emailed me and made various suggestions --your efforts are very much appreciated. So we can now cross that off of the list.

Now it is time to get serious about putting the FPM5 into a case. I have noodled what the case should look like at completion and made it large --10 X 13 X 4. The basic metal work was completed today and now it is time to arrange the various circuit boards. My first pass has enlightened me that I will need to make a few adjustments such as placing some of the circuit boards in a vertical position. Realizing this could happen I made the widths of the boards so that they could be installed in a vertical position. In some ways this will also facilitate shielding and will place the boards in a position for maintenance and adjustment. The template was first set with my KWM-4 project.

Here is a sneak peek at the enclosure:

Front Panel

Front Panel Close Up

Side view of board real estate area

Oblique view of the Front Panel

Fit Check of Circuit Boards. This is a good view of the original FPM300 Mainboard